AlllDfc. 3 T 3 b L

NBSIR 83-2803

Analysis of Electrical Fire

Investigations in Ten Cities

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Washington, DC 20234

December 1983

Final Report

—QC

100

. U56

03-2803

1933

Sponsored by:

U.S. Consumer Product Safety Commission

Washington, DC 20207

Uationai bureau or standards

library

NBSIR 83-2803

ANALYSIS OF ELECTRICAL FIRE

INVESTIGATIONS IN TEN CITIES

I 06

u6 ^

John R. Hall, Jr., Richard Bukowski and Alan Gomberg*

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Washington, DC 20234

December 1983

Final Report

•Present Address: Firepro, Inc., P.O. Box 145, Wellesley Hills, MA 02181

Sponsored by:

U.S. Consumer Product Safety Commission

Washington, DC 20207

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

vv

TABLE OF CONTENTS

Page

List of Figures v

List of Tables.. vi

Abstract 1

1. INTRODUCTION 1

2. DESCRIPTION OF WORK 3

3. OVERVIEW OF CHARACTERISTICS OF FIRE INCIDENTS 4

3.1 Fixed Property Use 4

3.2 Area of Origin 4

3.3 Equipment Involved in Ignition and Form of Heat of

Ignition 6

3.4 Detector Performance 6

3.5 Extent of Flame Damage... 8

3.6 Time of Fire..... 8

3.7 Occupant Condition 8

3.8 Comparison with National Fire Data..... 8

4. OVERVIEW OF ELECTRICAL SYSTEMS 11

4.1 Electrical Component Involved in Ignition 11

4.2 Alterations 14

4.3 Prior Problems with System 16

4.4 Code Violations 16

4.5 Fire Occurrence at Splice or Connection 22

4.6 Panel Board Location, Shelter from the Elements and

Ambient Conditions.. 22

4.7 Wiring Method, Material and Size 22

4.8 Specific Component Failure Causing the Fire 25

4.9 Presence and Effect of Grounding 25

5. CHARACTERISTICS AND PERFORMANCE OF OVERCURRENT PROTECTION

DEVICES 25

5.1 Performance of the Overcurrent Protection Devices 32

5.2 Overcurrent Protection Devices by Component Involved

in Ignition 34

5.3 Overcurrent Protection Device Rating by Minimum Wire

Size of Branch Circuit 34

iii
6 . THE ROLE OF BUILDING AGE 39

6.1 Age of Building versus Age of System, Circuit, and

Component 39

6.2 Fuses and Circuit Breakers by Age of Building 39

6.3 System Alterations by Age of Building 43

6.4 Components Involved in Ignition by Age of Building 43

6.3 Wiring Method by Age of Building 48

7. THERMAL INSULATION 48

8 . SERVICE COMPONENT FIRES 50

9. BRANCH CIRCUIT WIRING FIRES 50

10. CORD AND PLUG FIRES 51

11. SWITCHES, OUTLETS AND RECEPTACLES 52

11.1 Age of Building and Overcurrent Protection Devices 52

11.2 Problems with Splices and Connections 54

11.3 Grounding 54

11.4 Other Factors 55

12. LIGHT FIXTURE, LAMPHOLDER AND PORTABLE LAMP FIRES 55

13. CONCLUSIONS 55

14. ACKNOWLEDGEMENTS 56

15. REFERENCES 57

iv
LIST OF FIGURES

Figure 1. Tampering by Year Built and Type of Overcurrent

Protection Device
LIST OF TABLES

Page

Table 1. Electrical Fire Cases by City 2

Table 2. Area of Origin 5

Table 3. Equipment Involved in Ignition versus Form of Heat

of Ignition 7

Table 4. Time of Fire and Component Involved in Ignition 9

Table 3. Fixed Property Use Comparison 10

Table 6. Equipment Involved in Ignition Comparison 10

Table 7. Extent of Flame Damage Comparison 12

Table 8. Electrical Component Involved in Ignition 13

Table 9. Cases with Altered or Replacement Component or Circuit and Effects of Alterations 15

Table 10. Fire Incidents Where Electrical Systems Needed

Repairs, by Component Involved in Ignition.. 17

Table 11. Summary of Prior Problems 18

Table 12. Fire Incidents Where Code Violations Were Found,

by Component Involved in Ignition 19

Table 13. Frequencies of Code Violations Found 20

Table 14. Fire Involving Splices, Connections or Terminations, by Component Involved in Igniti’on 23

Table 15. Fires at Splices, by Component Involved in Ignition 23

Table 16. Copper versus Aluminum Wiring, by Component Involved

in Ignition, for Post-1964 Housing 24

Table 17. System Alterations, by Wiring Method 26

Table 18. Wiring Method and Component Involved in Ignition 27

Table 19. Branch Circuit Conductor Wire Sizes (A.W.G.) 28

Table 20. Failure Mode by Component 29

Table 21. Presence and Effect of Grounding 30

Table 22. Type of Overcurrent Protection Device 31

vi
Table 23. Overcurrent Protection Device Performance versus

Expectations 33

Table 24. Incidence of Unusual Conditions Found at Panel.... 35

Table 25. Overcurrent Protection Devices, by Component Involved

in Ignition 37

Table 26. Wire Size and Overcurrent Protection Device Rating,

by Type of Device... 38

Table 27. Overcurrent Protection Device Performance, by Type

and Rating of Device and Wire Size - Percentage of

Cases Where Device Interrupted Current.... 40

Table 28. Ratio of Electrical Fires to Housing Units, by Age of

Housing 41

Table 29. Age of Building versus Ages of Alteration, Involved

Component, Involved Circuit 42

Table 30. Need for Repair versus Age of Building, Alteration,

Involved Component, Involved Circuit 45

Table 31. Ratios of Fire Rates for Post-1940 and Pre-1940

Housing, by Type of Component Involved in Ignition 46

Table 32. Ratios of Fire Rates for Post-1960 and Pre-1960

Housing, by Type of Component Involved in Ignition....... 47

Table 33. Wiring Method by Building Age and Type of Overcurrent

Protection Device 49

Table 34. Details of Improper Location of Extension Cords 53

vii

ANALYSIS OF ELECTRICAL FIRE INVESTIGATIONS IN TEN CITIES

John R. Hall, Jr., Richard W. Bukowski and

Alan Gomberg*

Abstract

This report describes the results of an analysis of

electrical fire cases by the Center for Fire Research,

National Bureau of Standards for the Consumer Product

Safety Commission. The report describes the 105 detailed

electrical fire investigation reports from 10 participating cities and discusses findings resulting from analysis

of the data from those reports. These findings include

the effects of tampering, alterations and other system

problems, factors that may cause overcurrent devices to

fail to operate, the role of extension cords misused as permanent extensions of building wiring, the problems of

loose connections between receptacles and wiring, and

other scenarios and sequences of events that lead to

electrical fire ignition.

Key Words: Electrical fires

1 . INTRODUCTION

This report describes characteristics and patterns of 105 electrical

fires, with special attention to those patterns that suggest hypotheses on fire prevention programs and product design. Data for this analysis were

collected in 10 cities, as shown in table 1. The Consumer Product Safety

Commission (CPSC) sponsored the research and suggested an initial set of

issues to be examined. The Federal Emergency Management Agency, U.S. Fire

Administration (USFA) and its consultant, John Ricketts, collected the data

and implemented a training program on the identification of electrical fires

for fire department personnel in these 10 cities. The resulting detailed

electrical fire investigation cases were provided to the Center for Fire

Research (CFR) for review, coding and analysis. All electrical fires investigated occurred during the period of March 1980 through December 1981, but the

actual period of data collection varied from city to city.

The intent of this analysis was to identify patterns that could suggest

hypotheses regarding the nature of significant electrical failures, the

electrical distribution components involved in fire origination, and the

identification of the mechanisms resulting in component failure. These

results could then be used to assign priorities in further efforts aimed at

understanding electrical fire problems and the potential effects of actions

aimed at remedying those problems.

This analysis was done in two stages. The initial analyses, documented

in the Interim Report, used 110 cases, excluding only the Oakland case in ageof-building analyses for reasons cited later. In the second phase, five more

*Present address: Firepro, Inc., P.0. Box 145, Wellesley Hills, MA 02181

1
Table 1. Electrical Fire Cases by City

City

Akron, Ohio

Grand Rapids, Michigan

Long Beach, California

Oakland, California

Portland, Oregon

Sacramento, California

San Diego, California

San Francisco, California

San Jose, California

Toledo, Ohio

No. of Cases

22

4

8

1

10

13

7

16

11

13

Total 105

NOTE: An additional nine cases were provided. Four could not

be included in the analysis because of incomplete documentation and inadequate detail. Five fires were dropped after

completion of the Interim Report because a second-stage

analysis indicated they probably were not electrical in

origin.

2
cases were dropped because those fires were not of electrical origin. These

five cases have been removed from both the initial analyses and the new

analyses.

2. DESCRIPTION OF WORK

The detailed investigations used a fire incident report and a two-part

questionnaire, with one part containing general information on the electrical

system and the second part containing detailed information on the electrical

component involved. The questionnaire is not reproduced here due to its

length. Copies may be obtained from Linda Smith, U.S. Consumer Product Safety

Commission, Division of Hazard Analysis/Epidemiology, Washington, D.C.

20207. In addition, most of the cases included photographs and detailed

electrician's reports, including schematics of the buildings' electrical

systems and other relevant details. Approximately one third of the cases also

included damaged components.

The detailed investigations were made based on preliminary field

determination of electrical origin by the responding fire company and subsequent confirmation by fire investigators. After the completion of each

investigation, the completed questionnaires, photographs and samples were sent

to the USFA consultant, Mr. Ricketts, who reviewed them and contacted the

investigators as necessary to clear up questions and problems. The completed

cases were then passed to CFR, through CPSC, for coding and analysis.

The coding was screened by personnel skilled in electrical engineering,

who used the following procedure: The principal investigator coded each case,

using the investigator reports, photographs and physical samples where available. The points on which he felt further input was needed were identified.

An NBS electrical engineer then provided the needed input. (This procedure of

input only as deemed necessary was first tested on a random sample of ten

cases, with the electrical engineer reviewing all coding, not just items where

input was requested.) Input from the electrical engineer proved necessary in

approximately one third of the cases.

The computer coding was set up according to a three-part format which

also roughly corresponds to the organization of the material in this report.

First, the incident report data were coded using the data elements and con- ventions employed in the National Fire Incident Report System (NFIRS) [1]^.

(Most cities included incident reports prepared for NFIRS or using a similar

format.) Analyses of this information are contained in section 3 of this

report. Second were the general descriptions of electrical systems, based on Part 1 of the questionnaire. Analyses of this information are contained in

section 4 of this report. Third were the detailed descriptions of the particular electrical components involved in the fires. Analyses of patterns for

each major type of component are contained in sections 8 through 12 of this

report. Sections 5 through 7 of this report deal with issues that need to be

examined both relative to all components and relative to each major type of

^Numbers in brackets refer to the literature references listed at the end of

this paper.

3
component involved in ignition. These issues are characteristics and performance of overcurrent protection devices, the role of building age, and the role

of thermal insulation.

3. OVERVIEW OF CHARACTERISTICS OF FIRE INCIDENTS

This section presents some major patterns based on tabulations of key

Incident Report parameters. Subsequent sections present an overview of some electrical report information and more detailed examinations of failure modes

and key characteristics and present significant findings and hypotheses.

Following are brief definitions of the Incident Report parameters

examined.

Fixed Property Use - The type of property in which the fire occurred.

Area of Origin - The room or space where the fire originated.

Detector Performance - The presence or absence of smoke detector(s) and

their functioning.

Extent of Flame Damage - The final extent of flame and heat damage due to

the fire.

Time of Fire - Usually the time (often shortly after ignition) that the

fire was reported to the fire department.

Occupant Condition - A description of the occupancy of the structure just

prior to the fire (all occupants asleep, at least one occupant awake,

etc. )

.

Equipment Involved in Ignition - The equipment which provided the heat

which started the fire (fixed wiring, cord, plug, etc.).

Form of Heat of Ignition - The form of the heat energy igniting the fire

(water caused arc, arc from mechanical damage, etc.).

3.1 Fixed Property Use

Most cases (86 percent) were single family dwellings, with the remainder

either duplexes (eight percent) or small apartments (up to six units) (seven

percent). By design, no fires in large apartment complexes (containing over

six units) were investigated. This distribution compares well with national

Census estimates of occupied housing units for 1978, which indicate that 84

percent of the occupied housing that contains four or fewer individual units

are single unit and 16 percent are structures containing two to four dwelling

units [2]. In other words, there was no indication that some types of

housing, within this limited set, were more prone to electrical fires than

others.

3.2 Area of Origin

The area of fire origin was coded in NFIRS format. The results are tabulated in table 2. Concealed spaces - within ceiling, walls and attics -

4
Table 2. Area of Origin

Area Percent of Total

Bedroom 17.1

Living Room 7 .

Basement 7.6

Kitchen 6.7

Garage 4.8

Dining Room 1 .

Closet 1.0

Concealed Space - Wall 21.0

Concealed Space - Attic 15.2

Exterior Wall Surface 7.6

Concealed Space - Ceiling 5.7

Crawl Space 1.0

Other 2 .

Total 100.0

5
were the leading areas of origin, totaling 42 percent of all fires. Only 33

percent of the fires started in the normally occupied living areas, i.e.,

living rooms, bedrooms, kitchens and dining rooms.

As would be expected, the majority (73 percent) of branch circuit wiring

fires occurred in concealed spaces. Those that were not in concealed spaces

included legitimate locations, like wiring in basements with exposed rafters,

and illegitimate locations involving exposed wiring in places where wiring

should not be exposed. In addition, 56 percent of the fires involving

receptacles were in concealed spaces. (Fires that began behind the

switchplate in the receptacle were in concealed spaces. Fires caused by

receptacle faults but occurring outside the switchplate, for example in a plug, were coded as receptacle fires occurring in unconcealed spaces.)

Together these two components accounted for 73 percent of the concealed

space fires. For fires in living areas, the dominance of bedroom fires is

accounted for by cords and plugs, which were involved in 67 percent of the

bedroom fires. Almost half (44 percent) of the cord and plug fires in the

data base occurred in bedrooms.

3.3 Equipment Involved in Ignition and Form of

Heat of Ignition

These data elements are compared in table 3.

Several combinations of Equipment Involved and Form of Heat stand out in

table 3. Loose and faulty connections (38 percent of cases with known Form of

Heat) are the leading Form of Heat for fixed wiring, although mechanical

damage (22 percent of known cases), defective or worn insulation (19 percent

of known cases) and overloaded equipment (19 percent of known cases) are well

represented. Loose and faulty connections (62 percent of known cases) also

dominate the Equipment Involved category of switch, receptacle, outlet. The

cord and plug Equipment Involved category is dominated by mechanical damage

(46 percent of known cases) and overloaded equipment (33 percent of known

cases)

The other equipment categories have no dominant Form of Heat. Further

analysis of some of these patterns, using the more detailed data in the Part 1 and Part 2 reports, can be found in the subsequent sections, which address the

primary electrical components involved in ignition. The breakdown of this more detailed data is not directly comparable with the NFIRS type coding for

equipment involved, however, due to differences in the coding formats.

3.4 Detector Performance

The presence or absence of detectors was established in 94 of the 105 cases. They were present in 17 percent of the 94 cases. This compares with

the 1980 national estimates, which show detectors present in 20 percent of all

fires in one- and two-family dwellings and small apartments. The fact that

detectors are known to have been present in about one half of all households

in the country in 1980 [3] and were present in only 17 percent of the fires in

this data base indicates that homes with smoke detectors may be less likely to

6
Table

3.

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Involved

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Form

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have a reported electrical fire than homes without or that such homes may be more likely to control such fires without having to report them to the fire

department or both.

3.5

Extent of Flame Damage

The final extent of flame damage was known in all but two cases, and

flame damage was confined to the object of origin in 41 percent of the known

cases. Flames spread beyond the room of origin in only 10 percent of the cases

3.6

Time of Fire

As table 4 indicates, the time of fire is distributed differently for

each component involved in ignition. Some patterns, such as light fixture

fires occurring predominantly in the 6:00 p.m. to midnight period, are expected, but others, including the frequent occurrence of receptacle/outlet

fires in the morning hours and of branch circuit fires in the afternoon and

evening hours, are not so readily explainable. Attempts at examining these

distributions have not produced promising hypotheses.

3.7

Occupant Condition

Occupant condition at the time of ignition, while not an NFIRS data

element, was included on the incident report, and was known in 80 of the 105 cases. In 70 percent of these cases at least one occupant of the dwelling was awake and alert at the time of ignition. All occupants were asleep or impaired in 13 percent of the cases, and no one was home in 17 percent of the

cases.

3.8

Comparison with National Fire Data

National fire-cause distributions can be estimated from data in the

NFIRS, which contains computerized fire incident reports on fire causes and

fire losses from over 30 states. An attempt was made to compare the distributions of several key elements with national estimates calculated from the

NFIRS. Good correlation between national estimates and the study data was noted for the elements Fixed Property Use, Detector Presence and Equipment

Involved in Ignition. Substantial differences were noted for the element

Extent of Flame Damage. Finally, substantial differences found in two other

key elements, Area of Origin and Form of Material Ignited, are believed to be

due to differences in the application of the coding methodology. A discussion

of each element follows.

Fixed Property Use in the study data base was divided into three

categories - single family dwellings (excluding mobile homes), duplexes and

small apartments (up to six units). The distribution of Fixed Property Use in

the study data base was compared with the estimated national distribution of

similar categories from NFIRS, and the results are illustrated in table 5. No

major differences between the two data bases are noted.

Equipment Involved in Ignition, as indicated in table 6 (with unknowns

excluded) did not show large variances between the study data base and

national estimates. The nine Equipment Involved categories were generally in

8
Table 4. Time of Fire and Component Involved in Ignition

Midnight

- 6 a.m.

6 a.m. - Noon

Noon -

6 p.m.

6 p.m. - Midnight

All

Hours

Service Components (14%) 20% 20% 27% 33% 100%

Branch Circuit

Wiring (29%) 13% 13% 37% 37% 100%

Receptacles and

Outlets (26%) 22% 37% 22% 19% 100%

Cords and Plugs (17%) 11% 17% 33% 39% 100%

Light Fixtures (13%) 14% 7% 29% 50% 100%

All Components

(100%)*

* 16% 20% 30% 34% 100%

*Includes one low-voltage transformer case not included in other rows.

9
Table 5. Fixed Property Use Comparison

Fixed Property Use CPSC National Estimate

Single Family 86% 88%

Duplex 8% 5%

Apartment (up to six units) 7% 6%

Table 6. Equipment Involved in Ignition Comparison

Equipment CPSC Rank

National

Estimate Rank

Fixed Wiring 36% 1 39% 1

Cord, Plug 27% 2 19% 2

Switch, Receptacle, Outlet 15% 3 12% 3

Lighting Fixture, Lampholder 11% 4 12% 4

Lamp, Light Bulb 4% 5 7% 5

Overcurrent Protection Device 3% 6 6% 6

Other 2% 7 4% 7

Meter 1% 8 1% 8

Total 100% 100%

10
the same proportions for both, and their rank order is the same. This

indicates that the electrical components studied in detail here are represented in a similar manner to their relative national distribution as estimated from NFIRS.

As noted in section 3.4, Detector Presence was compared for the study

data and national estimates and was found to be similar.

A substantial difference between national estimates and study data was noted when Extent of Flame Damage was compared as indicated by table 7.

It is obvious from both the percentage distributions and the rankings of

Extent of Flame Damage that the study data base tends toward the smaller fires

much more than those in the NFIRS. This may be an artifact of the case selection process. In this study, emphasis was placed on detailed investigation,

so larger fires may not have been considered because extensive destruction of

the site often precludes detailed investigation. On the other hand, all fires are supposed to be reported to NFIRS. This suggests that property loss

figures from this study cannot be directly compared with national estimates.

The relatively high proportion (70 percent) of cases where occupants were awake and alert at ignition may also account in part for the relatively low

level of fire damage in the subject cases.

Significant discrepancies between the study data and national estimates

were found when Area of Origin and Form of Material Ignited were compared.

They are believed to be artifacts of the coding procedure, however, resulting

from a combination of more detailed and thorough investigation and analysis of

the study cases than is usual for the fire incidents in NFIRS, and the resulting ability to use a more exacting application of the coding procedures in the

study cases. In other words, the special-study codings are considered more

reliable on a case-by-case basis than the NFIRS codings, although the

distributions from the special study may be more or less representative than

the NFIRS distributions.

4. OVERVIEW OF ELECTRICAL SYSTEMS

This section contains overview information from the detailed electrical

fire investigation reports. Subsequent sections present more detailed information on selected parameters. These parameters are discussed separately from

the incident report elements because, in some cases, similar parameters coded

separately in the two reports are not directly comparable.

4.1 Electrical Component Involved in Ignition

Table 8 shows the Components Involved in Ignition for the 105 cases.

The first four categories (15 incidents) refer to utility system components tied to the particular building; they are usually located between the

building's final overcurrent protection device and those utility system com- ponents not tied to a particular building. The four categories are referred

to collectively as service components. In general, analysis of service comil
Table 7 . Extent of Flame Damage Comparison

Extent of Flame Damage CPSC

Obj ect 41%

Part Room 44%

Room 9%

Floor 6%

Building 1%

Outside Building 0%

100%

Rank

National

Estimate Rank

2 31% 1

1 20% 3

3 20% 3

4 6% 5

5 21% 2

6 2%

100%

6

12
Table 8. Electrical Component Involved in Ignition

Component Number of Incidents

Utility Supply Conductors 3

Overhead Utility Wires 3

Service Entrance Wiring - 1_ Service Entrance Cable 4

Service Entrance Conductors in Conduit 2

Meter, Meter Box, Meter Mounting 1

Service Equipment 4_ Service Entrance Conductor Termination 1

Grounding Electrode Conductor 1

Service Disconnect 2

Distribution Panel 1^ Feeder Wiring 1

Branch Circuit Wiring 30

Armored Cable (BX) 5

Nonmetallic Sheathed Cable (Romex) 14

Knob and Tube 9

Multiple Types 2

Cords and Plugs 27

Extension Cord 16

Cord on Appliance 7 Cord on Portable Lamp 1

Christmas Tree Wiring 1

Plug Adapter 1

Cord-Heating Device 1

Switch, Receptacle, Outlet 18

Wall Type Switch 1

Receptacle, Outlet 16

Baseboard Heater Thermostat 1

Lighting Fixture, Lampholder 14

Fluorescent Lighting Fixture 1

Incandescent Lighting Fixture 7 Lampholder 3

Portable Lamp 3

Low Voltage Transformer 1_ Low Voltage Transformer 1

Total 105

13
ponents was done on the group as a whole, as the limited number of fires

involving each individual component precluded more detailed analysis even at an exploratory level.

Of the remaining components, branch circuit wiring provided the most

cases, with nonmetallic sheathed cable and knob and tube dominating. Cords

and plugs, in particular extension cords, contributed significantly to the

total. Receptacles and outlets dominated their category, as did incandescent

lighting. Some light fixture incidents were not electrical system breakdowns

but were due to combustibles placed too close to otherwise normally operating

lighting equipment; this will be discussed further in subsequent sections.

4.2 Alterations

Overall, 72 percent of the electrical systems in this study had been

altered to some extent prior to the fire. These alterations ranged from minor

(such as extension of a circuit) to major replacement or modification of

system components. Some were system upgrades, such as replacement of deteriorated wiring or modernizing and upgrading system capacity, while others,

such as addition of bootleg circuits, splicing improper wiring into circuits,

or bypassing overcurrent protection devices had the effect of downgrading the

system.

Several assessments were made in the second-phase analysis of the nature

and effect of alterations. In the first-phase analysis, using the

investigator's reports, it was estimated that 20 percent of the cases involved

components that had been recently altered, rewired, replaced or installed. It was believed that this result understated the true extent of alterations and

replacements, so in the second-phase analysis the full case files were examined and an independent assessment of alteration and replacement was made. Table 9 indicates the percentage of cases, overall and by type of

component involved in ignition, that had alterations to the involved component

or the involved circuit or that showed involved components or circuits that were not the original components or circuits. Although 72 percent of all

systems had alterations, only 34 percent of involved components and 39 percent

of involved circuits showed alterations. Sixty percent of cases showed

replacement components, while 57 percent of cases showed replacement

circuits. Light fixtures had by far the highest rate of component alterations

(62 percent), while branch circuit wiring had by far the highest rate of

circuit alterations (60 percent). Receptacles and outlets showed a low rate

of component alterations (18 percent) but a high rate of replacement

components (72 percent).

Table 9 also shows an assessment, overall and by component, of the

effects of the alterations. Although some alterations were system

improvements, none were judged to have helped in preventing, delaying or containing the fire. A negative effect—making ignition more likely or fire

spread more likely, more widespread or more severe—was judged to have

occurred in 82 percent of the cases, while 18 percent were judged to have

produced no effect either way. Negative effects were most common for service

components (100 percent), least so for receptacles and outlets (60 percent

negative effect).

14
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15
The other side of the alteration question is to ask whether the systems

had had an unrecognized need for repairs prior to the fire. Table 10 shows

that 58 percent did, ranging from 27 percent of systems where cords and plugs were the involved components to 80 percent of systems where service components

were the involved components.

4.3 Prior Problems with System

Information on any problems involving the electrical system prior to the

fire incident was recorded by the investigator through discussion with the

building occupant. Some problems were noted immediately prior to (or simultaneous with) the ignition, while other problems appear to have occurred over extended periods of time.

Information on the presence or absence of prior problems was obtained in

97 percent of the cases; of these the existence of one or more prior problems

was noted 44 percent of the time. Of the 45 cases with at least one prior

problem, 69 percent had one, 22 percent had two, four percent had three, two

percent had four, and two percent had five or more prior problems. Overall,

in these 45 cases, a total of 65 specific problems were noted. Of the 18

different types of problems noted, the most common manifestation of a problem

was fuses blowing, followed closely by light flickering.

The noted prior problems undoubtedly represent a lower bound of those

actually occurring, because some respondents may not have remembered or may

have omitted reference to prior problems. One indication that this may have

occurred is that, although fuses blowing was noted as a problem by the

occupant in only 18 cases, overfusing was noted by the investigator in 31 cases.

Table 11 lists the categories of prior problems noted and their

frequencies. Some occurred singly, and others, as indicated earlier, occurred

in combination.

Efforts were made to correlate the most frequent prior problems with the

component involved in ignition, but no significant results were obtained.

Correlations with age of building are discussed in section 6.

4.4 Code Violations

Another perspective on the overall status of the electrical system was obtained by investigator assessments of the presence or absence of code violations. As table 12 shows, 61 percent of the fires occurred in homes with code

violations. This was least often the case for fires involving receptacles and

outlets (39 percent) or service components (47 percent). It was most often

true for fires involving light fixtures (86 percent) or branch circuit wiring

(70 percent).

Table 13 shows the particular code violations, in order of frequency.

Overfusing and overaraping occurred in nearly half of all systems having a violation. The next two most frequent violations - improper splice and cord

used to extend building wiring - are primarily or entirely problems of branch

circuit wiring. (See the next section for the dominance of branch circuit

wiring in splices.)

16
Table 10. Fire Incidents Where Electrical Systems Needed

Repairs, by Component Involved in Ignition

Component Involved

in Ignition

Total

Cases

Number of Cases Where Need for

Repair Was Relevant and Known

Percent Needing

Repair

Service Components 15 15 80

Branch Circuit

Wiring 30 28 75

Cords and Plugs 27 26 27

Receptacles and

Outlets 18 15 60

Light Fixtures 14 13 46

All Components 105 98 58

NOTE: The one case involving a low-voltage transformer as the component

is included only in the total.

17
Table 11. Summary of Prior Problems

(Prior Problems Noted in 44 Percent of the Cases)

Problem Description Number of Times Cited

Fuses Blowing 18

Lights Flickering 14

Lights Dimming 7 Breakers Tripping 6

Appliances Operating Slowly 3

Bulbs Burning Out Prematurely 3

Radio Sounding Scratchy 2

Sparking, Arcing at Outlet 2

Lights Going Out 1

Previous Similar Fire 1

Unable to Turn Off Light 1

Smoke and Heat at Receptacle 1

Hot Cord 1

High Electric Bills 1

Lights Failing to Turn On 1

Range Burners Burning Out 1

Lights Turning On and Off Due to Vibration 1

Unspecified 1

Total 65

18
Table 12. Fire Incidents Where Code Violations Were Found,

by Component Involved in Ignition

Component Involved in Ignition Number of Cases* Percentage with Violations

Service Components 15 47

Branch Circuit Wiring 27 70

Cords and Plugs 27 59

Receptacles and Outlets 18 39

Light Fixtures 14 86

All Components 102 61

*Not included are three branch circuit wiring cases where it was unknown

whether a code violation was present. The low-voltage transformer case is

included only in the totals.

19
Table 13. Frequencies of Code Violations

Number of Cases

Overloading 46

Overfusing or overamping 31

Overloaded extension cords 9

Overloaded fixed wiring or circuit 4

Undersized replacement appliance cord 1 #14 nonmetallic sheathed cable used as subfeeder

carrying 68 amps at 240 volts 1

Improper Extension of Building Wiring 14

Cord used to extend building wiring 13

Extension cord spliced into building wiring 1

Cords or Wires Run in Wrong Places 15

Cord stapled or attached to wall 5 Cord against or under furniture 2

Extension cord run through traffic area 2 Wire run through holes in wall 1 Cord run through hole in floor 1 Cord run through doorway 1 Cord run under rug 1 Overdriven staple on branch circuit cable 1 Lamp cord connected to surface 1

Exposed Wiring or Splices 7 Open or unprotected splices 4

Outlet box contained bare, unused hot wires 1 Exposed wiring 1 Armored cable out of connector 1

Improper Grounding 1_

Ungrounded system 3

Neutral connected to ground terminal in receptacle 1 Loose ground 1 Ground wire cut off 1 Faulty connection of a homemade grounding clamp 1

Defeated or Missing Overcurrent Protection Device

Penny behind fuse 2 Main circuit breaker bypassed 1 No overcurrent protection device 1

Other Mismatched Equipment and Improper Splices 18

Lamps too large for marked ratings of fixtures 3

Several extension cords spliced together without boxes 2 Extension cord spliced to lamp cord without a box 1 Extension cords spliced in several places due to

prior damage 1

20
Table 13. Frequencies of Code Violations (Cont'd)

Extension cord spliced to knob and tube wiring and

used to wire a duplex receptacle 1 Spliced service entrance connectors 1 #16 and #18 cords spliced together without a box

and on a 15 amp circuit 1 #14 and #12 wiring or cords spliced together on a 20 amp circuit 1 #14 knob and tube spliced to #12 nonmetallic

sheathed cable on 15 amp circuit 1 #18, #14 and #12 wiring or cords all spliced

together on 30 amp circuit 1 Industrial fluorescent fixture mounted directly

to subfluor, connected with #18 wire spliced to

#14 in open box 1 Pigtail from fixture looped to #14 wire without

connector 1 Knob and tube circuit tapped into using a crimp

connector improperly applied 1 Nonmetallic sheathed cable spliced to knob and tube

using only WRAP 1 Splice using WRAP and tape 1

Other Improper Installation 14

Bootleg circuits 3

Loose connections 2 Box mount fixtures secured to surface 2 Overtightened wire binding screw 1 Six wires on an ungrounded duplex receptacle 1 Two wires under one screw at fuse (double tap) 1 Electrical component mounted in inappropriate

enclosure made of combustible materials 1 Homemade lamp socket connected to plug and

inserted into receptacle 1 No bushing where cable entered box 1 Service entrance and meter socket covered with

stucco (water collected) 1

Other Violations 9

_ Unapproved electrical appliance fixed in place 1 Bad neutral at service entrance connection 1 Steel conductor 1 Unknown type 6

NOTE: Not shown here are four violations cited by local inspectors. These

violations could not be confirmed with the National Electrical Code

and may be local requirements. To maintain consistency, only

violations identified by CFR using the case files are listed.

21

i
A. 5 Fire Occurrence at Splice or Connection

The fire occurred at a wire termination, connection or splice in 33

percent of the cases. Of these, 97 percent were copper wiring and the remaining three percent (one case) were aluminum wiring. As indicated in table 14,

receptacles and outlets were the components where fires most often occurred at a wire termination, connection or splice.

Further examination of this point showed that actual splices were a problem primarily for branch circuit wiring, as shown in table 15. Of the 10

splice cases involving branch circuit wiring, four involved nonmetallic

sheathed cable, three involved knob and tube wiring, and the other three were divided among three other wiring methods.

4.6 Panel Board Location, Shelter from the Elements, and Ambient Conditions

The final overcurrent protection device for the branch circuit was in a panel board located on the exterior of the building in 32 percent of the 90

fires that did not involve service components. A panel board installed in the

interior of the building was provided in the other 68 percent of these

cases. Fused systems were located inside the building slightly more often

than circuit breakers. Shelter from the elements was provided in 86 percent

of the 29 cases with a panel board located on the exterior of the building.

No shelter was provided in 10 percent of the cases, and in three percent the

presence or absence of panel board shelter was unknown.

In 96 percent of the 90 fires not involving service components, the

ambient conditions at the panel board were judged to be normal for the area

and time of year. Two cases (two percent) were judged unusually hot, and two

cases (two percent) were judged unusually damp.

4.7 Wiring Method, Material and Size

Of the 90 fires not involving service components, nonmetallic-sheathed

cable (type NM, "Roraex") was used in 48 percent of the cases, knob and tube in

27 percent, electric metallic tubing (EMT) and armored cable (type AC "BX")

each in seven percent, and the remaining types of wiring, including multiple

types in a single circuit, in one or two cases each.

Copper wiring was used in 94 percent of the cases, aluminum wiring in

four percent and steel wiring in one percent. Most of the aluminum wiring

(three of the four cases) was found in housing built in or after 1965, and

aluminum wiring accounted for three of the 11 post-1964 cases (27 percent) not

involving service components. Table 16 shows the breakdown by component.

Nonmetallic-sheathed cable was used in the steel wiring case and three of

the four aluminum wiring cases; the fourth aluminum wiring case used service

entrance cable. The steel conductor case was especially puzzling since steel

conductors were never allowed by any code or standard and no one contacted had ever heard of steel cable being manufactured - even in wartime when copper was scarce. Luckily in this case, a sample was provided verifying the presence of

the steel conductors.

22
Table 14. Fires Involving Splices, Connections or Terminations, by Component Involved in

Ignition

Component

Percent of Fires at Splice,

Connection, Termination

Service Components 13

Branch Circuit Wiring 40

Cords and Plugs 26

Receptacles and Outlets 56

Light Fixtures 29

Transformer 0

Table 15. Fires at Splices, by Component Involved in Ignition

Component Involved in Ignition

Service Components

Branch Circuit Wiring

Cords and Plugs

Receptacles and Outlets

Light Fixtures

Transformer

Percent of Fires at Splices

0

31

75

70

23
Table 16. Copper Versus Aluminum Wiring, by Component

Involved in Ignition, for Post-1964 Housing

Component Involved

in Ignition

Branch Circuit Wiring

Cords and Plugs

Receptacles and Outlets

Light Fixtures

Total

Copper Wiring

0

3

2

3

8

Aluminum Wiring

0

1

2

0

3

Total Cases

0

4

4

3

11

24
Table 17 shows how the presence or absence of system alternations varies

by type of wiring method. The distribution of wiring methods is fairly close

to the expected distribution, given usage patterns in the 10 cities.

Table 18 shows the distribution of wiring method by component involved in

ignition.

Table 19 shows the relative frequency of wiring sizes of the involved

branch circuit conductors for all cases not involving service components, for

the smallest AWG size present in the circuit (Part A) and for the various

combinations found (Part B)

4.8 Specific Component Failure Causing the Fire

Table 20 shows the distribution of components whose failure caused the

fire by each of the major groups of components involved in ignition. For each

of these 89 cases (service components and the single transformer case are excluded) , the description of the component whose failure caused the fire was provided in a narrative, and the resulting 79 types of component failure

descriptions were organized into the 23 major groupings shown on the table.

Several analyses have been performed using these groupings, as described in

sections 8-12, and the tabulation in table 20 provides some insights in

itself. (For example, over half of the lighting fixture fires - those involving overlamping or combustibles too close - do not involve failures within the

electrical system.)

4.9 Presence and Effect of Grounding

The presence and effect of grounding for the system and the involved

circuit were examined for the 90 cases not involving service components. The

absence of grounding was established for either the system or the involved

circuit or both in 62 cases, as shown in table 21. Of these, the absence of

grounding was a factor in six cases — two involving only ungrounded circuits

and four involving ungrounded systems and circuits.

5. CHARACTERISTICS AND PERFORMANCE OF OVERCURRENT PROTECTION DEVICES

The distribution of cases among the different types of overcurrent

protection devices is as shown in table 22. Edison-base fuses and circuit

breakers dominated, and most of the analyses in this section concern only

them. Type "S" fuses are of interest because they cannot be overfused, but

because only one such case was found, it is included with Edison-base fuses in

all subsequent analyses.

Considering only fires that did not involve service components and only

fuses (both types) versus circuit breakers, there were 48 circuit breaker

cases (55 percent) and 39 fuse cases (45 percent). This contrasts sharply

with an expected split of 39 percent circuit breakers and 61 percent fuses,

based on each city's relative usage of fuses versus circuit breakers, as reported to Carolyn Kennedy, CPSC, by city officials and the International

Association of Electrical Inspectors.

25
Table

Wiring Method

17. System

Number of

Cases

Alterations,

Percent

by Wiring Method

Percent

Expected*

Percent with

Alterations

Nonmetallic Sheathed

Cable 43 48 33 70

Knob and Tube 24 27 29 71

Electric Metallic

Tubing 6 7 4 50

Armored Cable 6 7 2 100

Other** 11 12 12 91

Total 90 100 100 73

*Based on estimated percentages of use of each wiring method, by city. Data

obtained by Carolyn Kennedy, CPSC, from city officials and the International

Association of Electrical Inspectors.

**The category "other" includes individual conductors in both rigid and

flexible metal conduit, and those cases where more than one type of wiring

was used within the involved circuit. For percent expected, "other" refer

to systems with combinations of two or more wiring methods.

26
Table 18. Wiring Method and Component Involved in Ignition

Percentage of Wiring Methods

Nonmetallic

Sheathed

Cable

Knob and

Tube

Armored

Cable

Electric

Metallic

Tubing Other*

Number

of

Cases

Branch Circuit

Wiring 43% 27% 0% 17% 13% 30

Cords and Plugs 33% 33% 19% 0% 15% 27

Outlets and

Receptacles 61% 17% 6% 0% 17% 18

Lighting Fixtures 64% 29% 0% 7% 0% 14

Percentage of Components Involved in Ignition

Branch

Circuit

Wiring

Cords

and

Plugs

Outlets

and

Receptacles

Lighting

Fixtures

Number

of

Cases

Nonmetallic Sheathed

Cable 31% 21% 26% 21% 42

Knob and Tube 33% 38% 12% 17% 24

Armored Cable 0% 83% 17% 0% 6

Electric Metallic

Tubing 83% 0% 0% 17% 6

Other* 36% 36% 27% 0% 11

*The category "other" includes individual conductors in both rigid and

flexible metal conduit, and those cases where more than one type of

wiring was used within the involved circuit.

27
Table 19. Branch Circuit Conductor Wire Sizes (A.W.G.)

A. Wire Size Distribution (Smallest AWG Size in Circuit)

Wire Size Number Percent

6 2 8 2 10 2 12 21

14 57

16* 1

18* 1

Unknown 4 Total 90

2

2

2

23

63

1

1

4

100

B. Combinations of Wire Size

Number of Cases

6 only 2 8 only 2

10 only 1

12 only 20

14 only 51

10 and 8 1

12 and 10 1

14 and 12 6

16 and 12 1

18 and 14 1

Unknown 4

Total 90

*These cases, where smaller than normal wire was found within branch

circuits, had power cord/lamp cord spliced directly into the involved

branch circuit.

28
Table 20. Failure Mode by Component

Number and Percent

A. Branch Circuit Wiring (34% of Total) of Component

Mechanical damage or improper installation

(e.g., stapled, abraded, nailed, cut, other) 8 (27%)

Poor or loose splice (e.g., loose splice,

crimp, different wire types) 8 (27%)

Ground fault (e.g., water, ungrounded armored

cable, deteriorated insulation) 3 (10%)

Use of improper wiring in circuit

(e.g., steel, stranded) 3 (10%)

Knob and tube encapsulated 3 (10%)

Miscellaneous overload

(e.g., overloaded, short in range) 2 (5%)

Unknown 3 (10%)

B. Cords and Plugs (30% of Total)

Mechanical damage or poor splice

(e.g., to extension cord or appliance cord) 10 (37%)

Overloaded extension cord 6 (22%)

Overloaded plug 2 (7%)

Damaged plug (e.g., loose blade connector) 2 (7%)

Miscellaneous — plug (e.g., short, water) 2 (7%)

Miscellaneous — cord (e.g., deteriorated

insulation, electric blanket cord) 4 (15%)

Unknown 1 (4%)

C. Receptacles and Outlets (20% of Total)

Loose or poor connection 8 (44%)

Mechanical damage (e.g., cracked, fire) 3 (17%)

Overloaded 2 (11%)

Miscellaneous (e.g., deteriorated, miswired,

plug inserted improperly) 2 (11%)

Unknown 3 (17%)

D. Lamp and Lighting Fixtures (15% of Total)

Loose or poor connection or splice, miswiring 5 (36%)

Combustibles too close (e.g., ballast, cloth

fixture, towel, insulation) 5 (36%)

Overlamped 3 (21%)

Miscellaneous (e.g., deteriorated insulation) 1 (7%)

Note that the failure mode descriptions are highly dependent on the main

component, that is, mechanical damage to branch circuit wiring may be of a different nature than mechanical damage to cords.

29
Table 21. Presence and Effect of Grounding

Was the System

Grounded?

Was the Involved

Circuit Grounded?

Was the Lack of

Grounding a Factor?

Number i Cases

Yes Yes — 20

Yes Unknown — 2

Unknown Yes — 3

Unknown Unknown — 3

Yes No Yes 2

Yes No No 40

Yes No Unknown 2

No No No 4

No No Unknown 5

Unknown No No 5

Total 90

30
Table 22. Type of Overcurrent Protection Device

Type of Device Number of Fires Percent of Fires

Circuit Breakers

Edison Base Fuses

49

39

1

0

1

13

2

47

37

1

0

1

12

2

Type M S" Fuses

Cartridge Fuses

No Device Present

Not Applicable*

Unknown

Total 105 100

*In 13 of the 15 service component cases, the fire occurred outside the building's

overcurrent protection device, and so the type of device in use may not have

been relevant. In the other two service component cases, there were two separate

outside main breaker panels and the fire occurred in the connection between

them; therefore the type of devices used in these main breaker panels were

relevant for those cases.

31
5.1 Performance of the Overcurrent Protection Devices

An analysis was done of the possibility that some fuses and circuit

breakers failed to activate because the circumstances of the fire were such

that activation should not have been expected. Each case was reviewed and

judgments were made as to whether activation should have been expected, to

prevent ignition. Cases where activation would not have been expected

generally were cases involving a poor ground or a loose connection, both of

which are conditions that prevent an overcurrent condition from occurring at

the overcurrent protection device. Table 23 gives the results of this review,

and it shows that in most cases activation should not have been expected. Of

the 80 cases where an assessment was possible, only four (all fuses) would

have been expected to have activation to prevent ignition. (Note that these

expectations did not address the possibility of ignition at a remote location

permitted by a slow-acting or nonperforming overcurrent protection device.)

Of the 40 fuses, 16 (40 percent) interrupted the current, while 18 (45

percent) did not. For the remaining six fuses, three (eight percent) were believed to have operated only because fire attacked the circuit, and the

other three (eight percent) had unknown performance. Of the 49 circuit

breakers, 15 (31 percent) interrupted the current, while 24 (49 percent) did

not. For the remaining 10 cases, two (four percent) were believed to have

operated only because fire attacked the circuit, and the other eight (16

percent) had unknown performance.

Problems with the overcurrent protection devices were checked under two

headings - tampering and unusual conditions. Tampering generally referred to

conditions intended to defeat the overcurrent protection device, such as overfusing (or the analogous condition for circuit breakers, overamping)

putting a penny or other metal insert behind a fuse, wrapping a fuse with

foil, or having no protective device at all. Unusual conditions included all

the conditions covered under tampering and other problem conditions, such as exposed wiring, poor workmanship, ground cut-offs, double taps, and bootleg or jackleg circuits. ("Bootleg and jackleg circuits" are terms used on the west

and east coasts, respectively, to refer to multiple problems of a kind

associated with installations made by persons not knowledgeable of electrical

systems and codes.)

Tampering and unusual conditions found at the panel were almost universal

for the fuses. Of the 40 fuses, 33 (83 percent) were tampered with, four (10

percent) were not, and the tampering status was unknown for the other three

panels (seven percent). Similarly, unusual conditions were noted at the panel

in 35 (88 percent) of the cases, while three (seven percent) had none noted,

and the other two (five percent) were unknown. Of the 33 cases of tampering,

32 (97 percent) involved overfusing; the other case involved a penny behind

the fuse. Two of the cases with overfusing also involved a penny behind the

fuse.

By contrast, unusual conditions at the panel were not found for most

circuit breakers and tampering was comparatively rare. Of the 49 circuit

breakers, four (eight percent) were tampered with, and 42 (86 percent) were

not. The tampering status was unknown in the other three cases (six

percent). Similarly, unusual conditions were noted in 12 (24 percent) of the cases and were not found in 36 (73 percent) of the cases. The other one (two

32
Table

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attacked

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circuit

or

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percent) was unknown. All four cases of tampering involved overamping (i.e.,

overfusing of circuit breakers) . In two of these cases the circuit breakers

did automatically trip initially, but occupants reset them.

Of the 16 cases not cited as involving fuses or circuit breakers, one of

the two cases with device cited as unknown was also cited as overfused and was stated to have been reset. The one case with no device was cited for

tampering in that the circuit was left unprotected. Table 2A shows the type

of unusual panel conditions cited.

In summary, the vast majority (76 of 80) of incidents involved conditions

where the overcurrent protection device would not have been expected to

prevent ignition. In a minority of these incidents, the overcurrent

protection device did eventually activate but only after fire initiation had

occurred.

5.2 Overcurrent Protection Devices by Component Involved in Ignition

Table 25 shows how the type, problems and performance of overcurrent

protection devices varied across the four major types of components involved

in ignition. Fires involving branch circuit wiring, cords and plugs, and

lighting fixtures were fairly evenly distributed between fused and circuitbreaker-protected systems, but fires involving switches and receptacles were

three times as likely to be circuit-breaker-protected as fuse-protected. This

correlates with the fact (noted later in this report) that switch and

receptacle fires were much more evenly distributed by building age than were other fires, and the newer buildings, which tended to have lower rates of all

other types of fires, were also much less likely to have fuses. System

alterations were more common in branch circuit wiring fires than in fires

involving other types of components. Tampering and unusual panel conditions

were noted less often in cord and plug fires and switch and receptacle fires

than in branch circuit wiring or lighting fixture fires.

5.3 Overcurrent Protection Device Rating by Minimum

Wire Size of Branch Circuit

Table 26 compares the rating of the overcurrent protection device to the

smallest AWG size of the wire used in the branch circuit conductors supplying

current to the component involved in ignition. Thirty-three (89 percent) of

the 37 fuse cases with copper wiring of known size showed overfusing, but only

two (5 percent) of the A3 circuit breaker cases with copper wiring of known

size showed overamping.* The overall percentage with overamping was AA

percent. Two of the three aluminum wire cases with known wire size also

showed overamping.

*This is based on the following criteria: For copper wire, 1A gauge wire can support up to 15 amps, 12 gauge wire up to 20 amps, 10 gauge wire up to 30

amps, 8 gauge wire up to AO amps, and 6 gauge wire up to 50 amps. For

aluminum wire, 12 gauge wire can support up to 15 amps and 8 gauge wire up to

30 amps.

3A
Table 24. Incidence of Unusual Conditions Found at Panel

(Unusual Conditions were Noted in 53 Percent of the Cases)

Fuses

A. Individual Conditions

Overfusing

Ground cut-off

Bootleg/jackleg circuits

Double taps

Poor workmanship

Defeated

Fused neutral

B. Combinations of Conditions

Overfusing alone

Overfusing and double taps

Overfusing and ground cut-off

Overfusing and bootleg/jackleg circuits

Overfusing and poor workmanship

Overfusing and defeating

Overfusing, double taps and

bootleg/jackleg circuits

Overfusing, poor workmanship and

ground cut-off

Overfusing, bootleg/jackleg circuits,

and ground cut-off

Overfusing, poor workmanship and

bootleg/jackleg circuits

Overfusing, poor workmanship and

fused neutral

Defeated, bootleg/jackleg circuits and

ground cut-off

Total Number of Percent of

Conditions Cited Total

34

8

76

5

2

JL

63

54

11

11

9

8

3

2 100

Percent of

Number of Cases Total

15 42

4 11

4 11

2 6

1 3

1 3

2 6

2 3

1 3

1 3

1 3

_1

35

3

100

35
Table 24. Incidence of Unusual Conditions Found at Panel (cont’d.)

A. Individual Conditions

Circuit Breakers

Total Number of

Conditions Cited

Percent of

Total

Poor workmanship

Ground cut-off

Bootleg/j ackleg circuits

Overamping

Double taps

Fused neutral

Defeated

Exposed wiring

B. Combinations of Conditions

7 33

4 19

4 19

2 10

1 5 1 5

1 5 _1 5

21 100

Percent of

Number of Cases Total

Overamping alone 2

Poor workmanship alone 1

Fused neutral 1

Bootleg/j ackleg circuits 1

Poor workmanship and ground cut-off 2 Poor workmanship and bootleg/j ackleg circuits 1

Defeated and ground cut-off 1

Poor workmanship and exposed wiring 1

Poor workmanship, double taps and

bootleg/j ackleg circuits 1

Poor workmanship, bootleg/j ackleg

circuits and ground cut-off _1

12

17

8

8

8

17

8

8

8

8

8

100

Other

Unknown device: 1 with overfusing, poor workmanship and bootleg/j ackleg circuits

1 with poor workmanship and bootleg/j ackleg circuits

No device present: 1 with unprotected circuits, exposed wiring and bootleg/

j ackleg circuits

36
Table 25. Overcurrent Protection Devices, by

Component Involved in Ignition

Fuses

Circuit

Breakers Combined

Branch Circuit Wiring

Number of Fires 17 13 30

Fires 57% 43% 100%

Tampering 82% 17% (of 12) 57% (of 29)

Unusual Panel Conditions 88% 31% 63%

System Alterations 82% 85% 87%

Device Interrupted Current 71% (of 14) 38% (of 8) 50% (of 22)

Cords and Plugs

Number of Fires 11 15 26

Fires 42% 58% 100%

Tampering 88% (of 8) 0% (of 14) 32% (of 22)

Unusual Panel Conditions 90% (of 10) 20% 48% (of 25)

System Alterations 64% 67% 65%

Device Interrupted Current 40% (of 10) 54% (of 13) 48% (of 23)

(One case, not shown above, involved a device of unknown type.)

Switches and Receptacles

Number of Fires 4 13 17

Fires 24% 76% 100%

Tampering 100% 15% 35%

Unusual Panel Conditions 100% 23% 41%

System Alterations 50% 77% 71%

Device Interrupted Current 50% 30% (of 10) 36% (of 14)

(One case, not shown above, had no overcurrent protection device.

)

Lighting Fixtures

Number of Fires 7 7 14

Fires 50% 50% 100%

Tampering 100% 0% 50%

Unusual Panel Conditions 100% 29% 64%

System Alterations 71% 57% 64%

Device Interrupted Current 0% (of 5) 29% 17% (of 12)

Note: The numbers in parentheses indicate that the percentages in question are based on less than the full number of cases. Such entries reflect exclusions of unknowns (i.e., unknown whether tampering was present, unknown

whether unusual conditions were present, or unknown whether device interrupted current) and exclusions of cases where the overcurrent protection

device was believed to have operated only because the fire attacked the

circuit

37
Table 26. Wire Size and Overcurrent Protection

Device Rating by Type of Device

(Smallest AWG Size in Circuit)

6 8

AWG Wire

10

Size

12 1A 16/18*

Fuses

15 amp 0 0 0 1 2 0

20 amp 0 0 0 1 6 0

25 amp 0 0 0 2 A 0

30 amp 0 0 0 2 18 1

40 amp 0 0 0 0 0 0

50 amp 0 0 0 0 0 0

Total 0 0 0 6 30 1

Circuit Breakers

15 amp 0 0 0 4 2A 0

20 amp 0 0 1 9 1 1

25 amp 0 0 0 0 0 0

30 amp 0 0 0 0 0 0

40 amp 0 1 0 0 0 0

50 amp 2 0 0 0 0 0

Total 2 1 1 13 25 1

Combined Data

15 amp 0 0 0 5 26 0

20 amp 0 0 1 10 7 1

25 amp 0 0 0 2 A 0

30 amp 0 0 0 2 18 1

A0 amp 0 1 0 0 0 0

50 amp 2 0 0 0 0 0

Total 2 1 1 19 55 2

Note: These figures cover only copper-wire cases and exclude the service component

cases. Also excluded are one case where the type of device was unknown, one Edison-base fuse case where the rating of the fuse was unknown, and one circuit breaker case where the wire sizes were unknown.

The four aluminum wiring cases involved two with 20 amp circuit breakers and

12 gauge wire, one with a 30 amp circuit breaker and 8 gauge wire, and one with a 60 amp circuit breaker and wire of unknown size. The one steel wiring

case involved a 20 amp fuse and 14 gauge wire.

*These cases, where smaller wiring than normal was found within branch circuits,

had power cord/lamp cord spliced directly into the involved branch circuit.

38
Table 27 provides a further examination in terms of whether the

overcurrent protection device operated, given the type of device, the rating

of the device and the size of the wire.

6. THE ROLE OF BUILDING AGE

Older buildings accounted for a disproportionately large share of the

fires examined, but building age was highly correlated with several other

factors, so there is no clear indication of which factor(s) was the leading

element in raising the risk of electrical distribution fire. Table 28 shows

the increase in fire rate as building age increased. The fire rate for housing constructed in the 1950s is about equal to the fire rate for all housing,

which is nearly three times the fire rate for housing built in the 1960s and

1970s and just over half the fire rate for housing built before 1940.

6.1 Age of Building Versus Ages of System, Circuit and Component

Some attempts were made to examine age measures more closely related than

building age to the electrical system, particularly those parts involved in

fire. Age of last alteration was examined for systems that had been altered,

but age was available for only 14 cases, as shown in table 29. Of these, 11 had been altered within 10 years of the fire. In fact, 10 had been altered

within five years of the fire. Ages of involved component and involved

circuit also were determined, but 42-48 percent of the cases had unknown

ages. For those that were coded, the median age of involved component was 9.5

years and the median age of involved circuit was 15 years.

6.2 Fuses and Circuit Breakers by Age of Building

Fuses were phased out of most housing after 1950, and this is borne out

by an examination of the use of fuses versus circuit breakers in pre-1950

versus post-1950 buildings. Of the 28 fires in buildings built between 1950

and 1980, 22 buildings (79 percent) had circuit breakers while only four (14

percent) had fuses, and no building built after 1959 had fuses. Two had power

company fuses. By contrast, of the 73 fires in buildings built before 1950,

34 (47 percent) had fuses and 26 (36 percent) had circuit breakers. A total

of 10 had power company fuses only, one had an unknown type of device, and one had no device. Thus, the housing stock of the pre-1950 period shows slightly

greater presence of fuses than circuit breakers, while the housing stock of

post-1950 shows fuses to be a minor factor.

The problem noted earlier involving failures of untampered circuit

breakers to interrupt the current was slightly more prevalent in older housing. In six of the 19 fires (32 percent) involving untampered circuit

breakers in housing built in or after 1950, the current was interrupted by the

circuit breakers. Correspondingly, in five of the 22 fires (24 percent)

involving untampered circuit breakers in housing built before 1950, the

circuit breakers acted to interrupt the current. (Included in the base are five cases where it was not determined whether the circuit breaker had

operated and two cases where the fire attacked the circuit and this was believed to have caused the circuit breaker to operate. These seven cases

split fairly evenly, four before 1950 and three after.)

39
Table 27 . Overcurrent Protection Device Performance, by Type and

Rating of Device and Wire Size - Percentage of Cases

Where Device Interrupted Current

(Smallest AWG Size in Circuit)

AWG Wire Size

6/8/10 12 14 16/18

Fuses

15 amp * 100% (of 1) 50% (of 2) * 20 amp * 0% (of 1) 60% (of 5) * 25 amp * 100% (of 1) 33% (of 3) * 30 amp * 50% (of 2) 40% (of 15) 0% (of 1)

40 amp * * * * 50 amp it * * *

Circuit Breakers

15 amp * 50% (of 4) 44% (of 18) * 20 amp * 13% (of 8) 100% (of 1) 100% (of 1)

25 amp it * * * 30 amp it * * * 40 amp * * * * 50 amp 50% (of 2) * * *

Combined

15 amp * 60% (of 5) 45% (of 20) * 20 amp * 11% (of 9) 67% (of 6) 100% (of 1)

25 amp * 100% (of 1) 33% (of 3) * 30 amp * 50% (of 2) 40% (of 15) 0% (of 1)

40 amp * * * * 50 amp 50% (of 2) * * *

*No such cases

Note: Excluded from this table are all the cases excluded from table 27 and all cases where either the fire caused the device to operate or it was unknown

whether the device operated.

In the aluminum wiring case with unknown wiring size, it also was unknown

whether the circuit breaker operated. In the other three aluminum wiring

cases, the circuit breaker did not operate. In the steel wiring case,

the fuse did operate.

40
Table 28. Ratio of Electrical Fires to Housing Units, by Age of Housing

Year of

Construction

Age of

Housing

in 1980

Estimated Percentage*

of All Housing Units

with that Age

Percentage of**

Fires in Housing

of that Age

Index-Rat io***

of Fires to

Housing Units

1970-79 1-10 yrs 21.8 6.9 0.32

1960-69 11-20 yrs 21.5 6.9 0.32

1950-59 21-30 yrs 14.7 13.9 0.95

1940-49 31-40 yrs 11.0 14.9 1.35

Pre-1940 Over 40 yrs 31.0 57.4 1.85

Total 100.0 100.0 1.0

* The percentage distribution for housing units built before 1970 is based

on Census figures for housing units in the cities used in the study, i.e.,

of all housing built before 1970 in those cities, 27.4 percent was built

in 1960-69, 18.9 percent in 1950-59, 14.1 percent in 1940-49, and 39.6

percent before 1940. Because similar figures for those particular cities

were not available for the period of 1970-79, the national Census figure

of 21.8 percent was used, and then the study cities' distribution of

pre-1970 housing units was prorated over the 78.2 percent of all housing

built before 1970. A check of national figures for pre-1970 periods

suggest the cities' distribution is not significantly different from the

national distribution [2]

.

** Based on 101 study fires. This total excludes three fires where building

age was not recorded and the only fire in Oakland. The latter was excluded

on the theory that it would not be appropriate to include all the housing

units in Oakland in the building age just to accommodate one fire.

*** The index indicates how much higher or lower than the overall fire rate

was the fire rate for a particular building age cohort.

41
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Tampering with the overcurrent protection device is correlated with

building age primarily because use of fuses is correlated with building age,

as figure 1 demonstrates. Of the 26 fires in buildings built in 1950 or after

and having fuses or circuit breakers, three of the four buildings with fuses were tampered with, while only one of the 22 buildings with circuit breakers

were tampered with. This gives an overall tampering rate of at least 15

percent (four out of 26). (The qualification "at least" is needed because in

two circuit breaker cases the report did not indicate whether tampering had

occurred.) Of the 60 fires in buildings built before 1950 and having fuses or circuit breakers, 28 of the 34 with fuses were tampered with while only three

of the 26 with circuit breakers were tampered with, producing an overall

tampering rate of at least 52 percent (31 out of 60). (Again, the result is

qualified because in four fuse cases and one circuit breaker case it was not

determined whether tampering had occurred.)

The pattern for unusual conditions (overfusing, poor workmanship, double

taps, bootleg circuits, etc.) found at the panel closely paralleled the

pattern for tampering; both were correlated with building age primarily

because the most common unusual condition found, overfusing, is more common

for fuses than circuit breakers and fuses are more common in older

buildings. Of the 26 fires in buildings built in 1950 or after and having

fuses or circuit breakers, unusual conditions were found at the panel in three

of the four buildings with fuses, while they were noted in only four of the 22 cases with circuit breakers. This gives an overall unusual conditions rate of

at least 27 percent for buildings built in 1950 or later. (This qualification

is needed because in one of the circuit breaker cases, it was unknown if

unusual conditions existed.) Of the 60 fires in buildings built prior to 1950

and having fuses or circuit breakers, unusual conditions were found in 30 of

the 34 cases with fuses compared to seven of the 26 with circuit breakers.

This gives an overall unusual conditions rate of at least 63 percent for

buildings built prior to 1950, again most likely due to the frequency of

overfusing found. (The qualification is needed because in one fuse case and

one circuit breaker case, it was unknown whether unusual conditions were

present .

)

6.3 System Alterations by Age of Building

As expected, system alterations were rare in new buildings, common in

somewhat older buildings, and almost universal in very old buildings. Of the

14 buildings built in the 1960s and 1970s, only five (36 percent) had had - alterations. Of the 54 buildings built in the 1930s, 1940s, and 1950s, however, 37 buildings (69 percent) had had alterations. And of the 33 buildings

built prior to 1930, 31 (94 percent) had had alterations.

The other side of alterations is need for repair, and the need for repair

showed a significant increase for buildings over 20 years old, as table 30

shows. When age of involved component or involved circuit is used as the

measure, however, the increase in need for repair occurs closer to the 30-year

point.

6.4 Components Involved in Ignition by Age of Building

Tables 31 and 32 show that the involvement of some classes of components

changed dramatically at 1940 or at 1960. The most notable patterns are for

43
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45
Table 31. Ratios of Fire Rates for Post-1940 and Pre-1940

Housing, by Type of Component Involved in Ignition

Type of

Component

Involved in

Ignition

Housing Units Built in

1940 Or After

Housing Units Built

Before 1940

Number of

Fires

Percent of

Fires

Number of Percent of

Fires Fires

Ratio of Fire Rate

for Pre-1940 Housing

Units to Fire Rate

for Post-1940 Housing

Units*

Service

Equipment 3 21 11 79 8.2

Branch

Circuit

Wiring 14 50 14 50 2.2

Cords and

Plugs 10 37 17 63 3.8

Switches and

Receptacles 10 56 8 44 1.8

Lighting

Fixtures 6 46 7 54 2.6

All

Components 43 43 58** 57 3.0

* This is given by the ratio of the prior-to-1940 and after-1940 percentages,

divided by .449, which is the ratio of housing units built prior to (31.0%)

and after 1940 (69.0%), as noted in table 29. ** The total includes one low-voltage transformer case, which does not fit with

any of the major component groups.

46
Table 32. Ratios of Fire Rates for Post-1960 and Pre-1960 Housing,

by Type of Component Involved in Ignition

Ratio of Fire Rate

Type of

Component

Housing Units Built in

1960 or After

Housing Units Built

Before 1960

for Pre-1960 Housing Unit

to Fire-Rate for

Involved in

Ignition

Number of

Fires

Percent of

Fires

Number of

Fires

Percent of

Fires

Post-1960 Housing Units*

1

Service

Equipment

I 1 7 13 93 9.9

|: Branch

Circuit

Wiring

i

1 4 27 96 20.6

Cords

| and

Plugs 4 15 23 85 4.4

|j Switches and

Receptacles 5 28 13 72 2.0

t Lighting

Fixtures 3 23 10 77 2.5

All

Components

1

14 14 87** 86 4.7

*This is given by the ratio of the prior-to-1960 and after-1960 percentages,

divided by 1.309, which is the ratio of housing units built prior to (56.7

percent) and after 1960 (43.3 percent), as noted in table 29.
service equipment, which has a much larger share of its fires in pre-1940

housing than do the other component groups, and for branch circuit wiring,

which shows a similar dramatic change in fire rate at 1960. At the other

extreme, switches and receptacles show the smallest differences in fire rates

between old and new buildings.

6.5 Wiring Method by Age of Building

Table 33 presents the distribution of wiring method by age of building,

as given in the cases, and type of overcurrent protection device. The figures

exclude service component fires and the single low voltage transformer fire;

the figures on fuses include the type S fuse case. Nonmetallic sheathed cable

was present in most of the fires in buildings constructed in or after 1950 and

is nearly as common in fires in buildings constructed before 1950 as the

leading wiring method, knob and tube. Circuit breakers were used primarily

with nonmetallic sheathed cable, while fuses were used with nonmetallic

sheathed cable and knob and tube wiring. When electric metallic tubing was

used, it was solely with circuit breakers, and when armored cable was used, it was usually with fuses. The "other" category in table 33 is primarily made up

of hybrid wiring systems, that is a mix of multiple wiring methods within the

individual system.

7 . THERMAL INSULATION

There were 17 cases coded as involving thermal insulation at the point of

fire origin. No information was obtained on fires that could have involved

insulation but did not (e.g., fires in the vicinity of insulation but which

were not coded as having insulation involvement) , so no estimate can be made

of the percentage of insulation involvement in cases where that was a possibility.

Of these 17 cases, nine involved cellulose insulation, seven involved

mineral fiber insulation, and one involved insulation of unknown type. Of the seven cellulose insulation cases for which the installation date was known,

all had had the insulation installed within two years of the fire. Note,

though, that significant use of cellulose insulation is a relatively recent

phenomenon. Of the 16 cases involving known insulation types, one case of

cellulose insulation and one case of mineral fiber insulation involved service

components; a second case of mineral fiber insulation involved the one lowvoltage transformer case.

Of the 14 cases involving non-service components and known insulation

types, two of the cellulose-insulation cases were coded with failure mode and

contribution to fire unknown or not applicable. That leaves six cases each of

cellulose and mineral fiber insulation. All six cellulose-insulation cases involved encapsulation, that is, a heat buildup leading to fire caused by the

fact that insulation surrounded the wiring. For half these cases,

encapsulation was the only problem, while for half it occurred in combination

with electrical problems. Two thirds of the mineral fiber cases involved

encapsulation as the only problem; the rest involved only electrical

problems. All six cellulose-insulation cases showed the insulation

contributing to both early ignition and fire spread. Only one third of the

mineral fiber cases contributed to both stages; the rest contributed only to

early ignition.

48
Table 33. Wiring Method, by Building Age and Type

of Overcurrent Protection Device

(Excluding fires in service components or low voltage transformers)

A. All Fires

Wiring Method Circuit Breakers Fuses Other /Unknown Total

Nonmetallic sheathed

cable 60% 31% 50% 47%

Knob and Tube 13% 46% 0% 27%

Electric Metallic Tubing 13% 0% 0% 7%

Armored Cable 2% 13% 0% 7%

Other 13% 10% 50% 12%

Total 100% 100% 100% 100%

Number of Fires 48 39 2 89

(These totals include four fires not included below - three with age unknown

and the one fire from Oakland, which is not included in any distribution by

age for reasons given earlier.)

B. Fires in Housing Built Prior to 1950

Wiring Method Circuit Breakers Fuses Other/Unknown Total

Nonmetallic sheathed

cable 42% 27% 50% 34%

Knob and Tube 23% 48% 0% 36%

Electric Metallic Tubing 15% 0% 0% 7%

Armored Cable 4% 12% 0% 8%

Other 15% 12% 50% 15%

Total 100% 100% 100% 100%

Number of Fires 26 33 2 61

C. Fires in Housing Built in or After 1950

Wiring Method Circuit Breakers Fuses Other/Unknown Total

Nonmetallic sheathed

cable 86% 75% — 84%

Knob and Tube 0% 0% — 0%

Electric Metallic Tubing 10% 0% — 8%

Armored Cable 0% 25% — 4%

Other 5% 0% — 4%

Total 100% 100% — 100%

Number of Fires 21 4 0 25

Note: Percentages may not total to 100% because of rounding error.

49
Of the eight cellulose insulation fires not involving service components,

six (75 percent) involved branch circuit wiring and two were light fixture

fires. Of the seven mineral fiber insulation fires not involving service

components, four (57 percent) involved branch circuit wiring, while the other

three were evenly divided among receptacles, light fixtures, and low-voltage

transformer.

8. SERVICE COMPONENT FIRES

As noted earlier, the category of service components consists of utility

supply conductors, service entrance wiring, service equipment and distribution

panels. Service components were cited as the component involved in ignition

in 15 cases, or 14 percent of the total. As noted in section 5, service

component fires were relatively rare in buildings under 40 years of age. None

of the six cases involving service entrance wiring occurred in buildings less

than 40 years old.

No consistent single failure mode or contributor was noted for service

components. A total of five fires were attributed to deteriorated insulation,

with water accumulation noted in three cases. In four cases the primary

causal factor was given as improper installation of a recently altered system,

resulting in a ground fault or overload condition. Alterations in progress

were responsible for two additional fires, one resulting from accidental

contact with high voltage lines, and one from the removal of support for the

service entrance cable. Finally, four cases were essentially unknown, including two ground faults from unspecified failures.

One pattern of interest was by city. Akron accounted for 20 percent of

the total cases but 53 percent of the service-component fires. Over a third

of Akron's fires involved service components compared to eight percent for all

other cities combined. We were unable to identify any special conditions in

Akron that would account for this difference. It may be that the

investigators in Akron were more attuned to these kinds of fires and therefore

identified things the investigators in the other cities did not identify.

9. BRANCH CIRCUIT WIRING FIRES

Several aspects of fires involving branch circuit wiring have been

discussed in earlier sections. Several additional tabulations are discussed

here.

A total of 70 percent of the involved branch circuits contained at least some //14 AWG wire. This is roughly consistent with the wire size

distribution across all cases listed in table 19.

Most of the involved branch circuits were 120 volt (90 percent) and 80

percent were general purpose (lighting and receptacle) circuits. The

remainder were divided two-to-one between large and small appliance circuits.

In 12 cases (40 percent) one or more electrical components supplied by

the involved circuit were noted to be "on" at the time of the fire. (In four cases (13 percent) it was indicated that no electrical components were "on" at

ignition, and the remaining 14 cases (47 percent) were unknown.) The

50
connected circuit load on the involved branch circuit was known in only nine

of those 12 cases and for those cases, it ranged from three watts to 2,160

watts.

Overloading of the circuit was unknown in eight of the cases. Of the

remaining 22 cases, seven (32 percent) were noted to be overloaded. All of

the involved branch circuits had been damaged electrically, damaged by the

fire, or both. In addition, six were found to have been damaged mechanically,

two were corroded and one had multiple types of damage noted.

Finally, of the specific component failures causing the fire, mechanical

damage (most often by staples) and splice problems stand out.

10. CORD AND PLUG FIRES

Of the 27 fires involving cords and plugs, 16 (59 percent) involved

extension cords, six were permanently attached appliance cords, four were detachable appliance cords and one was a Christmas tree light cord.

As indicated in table 32, cord and plug fires showed more of a fire-rate

difference between pre-1940 and post-1940 buildings than did any other non- service component fires. This may be largely due to the use of extension

cords to extend outmoded, inadequate or defective branch circuit wiring in

older buildings. This hypothesis is supported by the fact that a cube tap or other device was used to extend the wiring of the building in 56 percent of

the cases. Also in all 16 extension cord cases, the cords were noted to be

replacing permanent building wiring.

The involved cord was plugged into a grounded receptacle in only six

cases, four of which were in buildings less than 15 years old. All of the

ungrounded receptacles were in buildings over 25 years of age, and 81 percent were in buildings over 40 years old.

Since the dominant problem in cords and plugs appears to be the use of

extension cords to replace building wiring, the remaining analysis in this

section focuses on them. The misused extension cords were also heavily used,

compounding the problem. Of the 16 extension cords, eight were beng used

daily, 24 hours per day; and another one was being used daily eight hours per

day. A total of three were used daily, four hours per day; one was used

daily, two hours per day; one was used about one hour per month; one had just

been put into use; and one was used daily for an unknown time. This pattern

of extensive operation was not very different from the pattern for appliance

cords, where four of nine cords with known usage rates were in use 24 hours

per day. Appliance cords, however, are often designed to stand up to heavy

use.

One half of the 10 appliance cord failures were at the plug, while only

one of the 16 extension cord failures occurred at the plug, possibly

indicating that the weak link in extension cords is the cord itself. A total

of 11 of the 16 extension cords were noted as lamp cord, while eight of the 10

cords used with appliances were noted to be the generally heavier duty

applicance or power cords.

51
While all of the seven appliance cords where cord age was known were over seven years old, only two of the 12 extension cords of known age were over seven years old. The remaining 10 were no more than five years old, and four were one year old or less. This indicates that, unlike appliance cords, the

effect of age in extension cords may be a secondary issue relative to the

issue of use, and misuse, of the cords.

Except for the predominance of plugs and older cords, there was no clear

pattern of specific failure mode for appliance cords. A clear pattern of

misuse of extension cords is indicated, however. The specific failure mode

was given as mechanical damage in 44 percent of the cases, overloading in 44

percent of the cases, and splicing in 12 percent. Although splicing was indicated as the specific failure mode in only two cases, at least seven and

possibly eight of the 16 extension cords had been spliced (versus only one of

the 10 appliance cords). The frequency of overloading fires is most likely

explained by the use of the cords to replace or extend building wiring. The

mechanical damage problem may be in part explained by cord location, as in 14

of the 15 cases where location was known, the extension cord was noted to be

improperly located, often in multiple ways. A summary of the ways in which

extension cords were improperly located is given in table 34.

The extension cord cases were reviewed in terms of whether ignition would

have been prevented by a line fuse in the cord, increased wire size, improved

insulation, or some combination of the three. Of the 16 cases, 11 would have

had ignition prevented by a combination of line fuse and increased wire size,

with improved insulation having no impact. These 11 cases typically involved

(a) intermittent overloading by devices like irons and hand-held hair dryers

that are not in continuous use and (b) encapsulation of the cord, which had

large segments running under boxes or rugs, pinned to the wall by a mattress,

or otherwise covered. Ignition would have been prevented if the cord were

able to handle its peak loads (increased wire size) or able to shut off if it

received a load it could not handle (line fuse). Of the other five cases,

three would have benefited from improved insulation, specifically improved

abrasion resistance, and a line fuse but did not need increased wire size.

(One case would have benefited from all three modifications and one would not

have benefited from any.) These three cases typically involved mechanically

damaged cords located in heavy traffic areas.

11. SWITCHES, OUTLETS AND RECEPTACLE

Fires in receptacles were more evenly distributed over building age than

fires in any other component involved in ignition, and this fact correlated

with a higher than usual percentage of fires occurring in homes with circuit

breakers. Terminations and connections were notable as problems, with at

least nine of the receptacle fires occurring at a termination or connection.

(Another case occurred at a splice, termination or connection, but it was unknown which of the three was involved.) This suggests that loose

connections between the receptacles and the wiring played a leading role in

ignition. Also, there was a notably low proportion of ungrounded receptacles.

11.1 Age of Building and Overcurrent Protection Devices

As noted in section 6, receptacle fires are much less concentrated among

older buildings than are other fires. For all fires, the fire rate in pre52
Table 34. Details of Improper Location of Extension Cords

(Improper location noted in 93 percent of cases where location was known)

Nature of Improper Location Frequency Noted

On floor in traffic areas Attached to building surfaces with nails, staples

Through doorways, windows, etc.

Under clothing, rugs, refrigerator

Wrapped around objects

Through holes in walls, floors

Close to heaters, hot objects

75

4

4

2

2

1

NOTE: Some cords had more than one feature of improper location. The

25 location problems correspond to 14 cases.

53
1940 buildings is three times the fire rate in post-1940 buildings, but for

receptacles the fire rate in pre-1940 buildings is less than twice as great.

Buildings built in or after 1960 account for 28 percent of receptacle fires

but only 11 percent of all other fires. This suggests that, relative to other

parts of the electrical system, receptacles have a larger share of problems

that are there from the beginning, as contrasted with problems that show up

only after the passage of decades.

Since fuses were largely phased out after 1950, the use of circuit

breakers correlates well with building age, and so receptacle fires show a significantly higher percentage of cases with circuit breakers present.

Receptacles were protected by circuit breakers in 72 percent of the cases versus 22 percent by fuses and six percent (one case) with no device. This

compares with 49 percent circuit breakers, 49 percent fuses and one percent

other or unknown devices in all other cases not involving service components

or low voltage transformers.

11.2 Problems with Splices and Connections

Receptacle fires accounted for a major share of fires at splices,

terminations, and connections. For receptacle fires, 56 percent were at

splices or connections, compared to 32 percent of all other fires, excluding

fires involving service components or low-voltage transformers, where only 13

percent of fires were at splices or connections. Focusing on terminations and

connections, 45-50 percent of receptacle fires occurred at such points,

compared to 13 percent of fires involving service components or low-voltage

transformers and 12-15 percent of all other fires. (The range reflects the

fact that, for some fires occurring at a splice or termination/connection, it was unknown which was involved.)

If this pattern of fires at terminations and connections suggests a pervasive problem with loose connections, the specifics of components whose

failure caused the fire strengthen that suggestion. Six of the 10 fires at

splices or connections (nine of which were copper wiring) definitely involved

loose connections. Two others had the component causing the fire listed as unknown or uncertain. The other two consisted of one case with an old, deteriorated outlet and one case with poorly installed aluminum wiring.

Of particular interest is the pattern for the four fires involving backwired receptacles. The four back-wired receptacle cases represent

approximately the expected proportion of the 17 receptacle cases where it was known how the receptacle was wired. Those four fires constitute 21 percent of

the receptacle fires, whereas 16 percent of homes in the study cities have

backwired receptacles, according to estimates provided by Carolyn Kennedy,

CPSC, based on discussions with city officials and the International

Association of Electrical Inspectors. Two of those four cases definitely

involved a loose connection, and a third involved a fire at a splice or connection where the component causing the fire was uncertain.

11.3 Grounding

Of the 16 receptacle fires where it was known whether the receptacle was grounded, eight were grounded (50 percent) and eight were not. The eight that were grounded consisted of four with the grounding conductor going directly to

54
the receptacle, one each with the conductor going to an isolated screw in the

outlet box or a grounding clip, and two involving some other arrangement.

Grounding was far more prevalent in newer buildings. In the seven buildings built in or after 1950, five (71 percent) had grounded receptacles - and

it was 80 percent for the five buildings built in or after 1960 - while only

three of the nine buildings built prior to 1950 (33 percent) had receptacle

grounding. (These calculations exclude the three cases where it was unknown

whether the receptacle was grounded.)

There were 12 cases involving metal outlet boxes where it was known

whether the box was grounded; it was not grounded in 67 percent of those

cases. The relationship to age was even more pronounced here. Of the four

buildings built in or after 1950, three (75 percent) had grounded outlet

boxes, while only one of the eight pre-1950 buildings (13 percent) did.

11.4 Other Factors

Several elements that had been considered likely to emerge as factors in

receptacle fires did not. Only one of the fires involved a receptacle located

near a heating unit and only one involved a receptacle surrounded by thermal

insulation. As table 9 showed, receptacles and outlets accounted for the

lowest percentage of alterations, although they did account for the highest

percentage of replacement components and replacement circuits.

12. LIGHT FIXTURE, LAMPHOLDER AND PORTABLE LAMP FIRES

Of the 14 fires involving light fixtures, lampholders and portable lamps,

13 involved incandescent, lights , and only one involved a fluorescent

fixture. The failure of the fluorescent fixture was due to the ballast being

installed too close to combustible material. Three of the remaining

incandescent light fires also were not electrical in nature, as two were

caused by the ignition of combustible material draped over lighted portable

lamps, and the third was the ignition of a home-made macrame fixture due to

over-heating. Of the remaining 10 fires, one resulted from a loose cord

connection in a portable lamp and the other nine involved light fixtures

permanently connected to building wiring.

Of these last nine fires, three were caused by overlamping of the light

fixture, and one related to the encapsulation of a light fixture by cellulose

insulation. Two cases involved porcelain lampholders - one caused by

deteriorated insulation and the other by a loose connection - and one case was

a jury-rigged metal and plastic fixture attached to the building wiring by

lamp cord with taped splices. The remaining two fixtures were permanently

connected; the failure mode was indicated as a loose splice in one, and in the

other it was an improper crimp in the supply to the fixture which energized

the fixture, igniting insulation. Of the last five cases (all electrical

failures in permanently connected fixtures) , two had been recently worked on, one had not, and the ether two were undetermined.

13. CONCLUSIONS

This analysis of 105 electrical fires has identified a number of patterns

that help to identify leading scenarios and factors in the ignition or

55
exacerbation of electrical fires. An important finding is that 61 percent of

the cases involved apparent violations of the National Electrical Code

(including its workmanship provisions), and these often were principal factors

in the occurrence of the fire.

In analyzing whether overcurrent protection devices would have been

expected to activate, it was found that of 80 cases where an assessment was possible, only four (all fuses) would have been expected to activate to

prevent ignition. These four cases all involved tampering with the fuses, and

in general tampering was widespread with fuses but not with circuit

breakers. The cases where devices would not have been expected to activate

generally involved loose connections or poor grounds, conditions that prevent

overcurrent conditions from occurring at the device.

In examining patterns for particular classes of components, it was found

that branch circuit wiring fires were much more likely in pre-1960 housing

than in post-1960 housing. Over half the cord and plug fires were due to

extension cords, always involving the use of extension cords to replace

permanent building wiring. Extension cord failures, unlike failures involving

other kinds of cords, tended to be in the cord rather than the plug. Most of

these cords would have benefited from a line fuse in the cord combined with

either increased wire size or improved insulation. Roughly half of all

receptacle fires were at loose connections, compared to roughly one in seven

of the other fires. There was some evidence that backwired receptacles have

higher fire rates and more problems with loose connections, but there were too

few such cases to support strong conclusions.

Service component fires were far more common in pre-1940 housing than in

post-1940 housing, but they also were concentrated in one of the 10 study

cities, suggesting that differences in the investigators' sensitivities may

have played a role. The question of alterations was examined from several

directions. Some beneficial alterations were found, but none of these helped

to make ignition less likely or spread less widespread or less severe, and

most alterations made the fire more likely, widespread, or severe. The

analysis was limited, however, by the gaps in information on the histories of

the involved electrical systems. Additional analysis of the system

descriptions in the electricians’ reports and summaries of overcurrent

protection may shed more light on this topic.

These findings can serve as a basis for prioritizing further efforts on

the nation's electrical fire problems.

1 4 . ACKNOWLEDGEMENTS

The authors gratefully acknowledge the substantial contributions of John

Ricketts for his review, clarification and compilation of the cases, and to

Linda Smith and Ed Krawiec of the U.S. Consumer Products Safety Commission,

for their advice and suggestions. Finally, the efforts of the numerous fire

service and electrical investigators in the cities of Akron, Grand Rapids,

Long Beach, Oakland, Portland, Sacramento, San Diego, San Francisco, San Jose

and Toledo, who provided the data for this study, are gratefully acknowledged.

56
15. REFERENCES

Uniform Coding for Fire Protection, 1976, NFPA No. 901, National Fire

Protection Assn., Boston, MA 02210, 1976.

Statistical Abstract of the United States: 1980, U.S. Bureau of the

Census, December 1980.

Fire in the United States, Third Edition, Federal Emergency

Management Agency, Washington, D.C. 20472, p. 44.
NBS-114A (rev. 2-80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

SHEET (See instructions) NBSIR 83-2803 December 1983

4. TITLE AND SUBTITLE

1

ANALYSIS OF ELECTRICAL FIRE INVESTIGATIONS IN TEN CITIES

5. AUTHOR(S)

John R. Hall, Jr., Richard Bukowski, Alan Gomberg

6. PERFORMING ORGANIZATION (If joint or other than N BS, see instructions)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

U. S. Consumer Product Safety Commission

Washington, D. C. 20207

10.

SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bl iography or literature survey, mention it here) This report describes the results of an analysis of electrical fire cases by the

Center for Fire Research, National Bureau of Standards for the Consumer Product Safety

Commission. The report describes the 105 detailed electrical fire investigation report i from 10 participating cities and discusses findings resulting from analysis of the data

from those reports. These findings include the effects of tampering, alterations and

other system problems, factors that may cause overcurrent devices to fail to operate,

the role of extension cords misused as permanent extensions of building wiring, the

problems of loose connections between receptacles and wiring, and other scenarios and

sequences of events that lead to electrical fire ignition.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

accident investigation; electrical fires; fire investigations; overcurrent; wires

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

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~] Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

65

15. Price

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